It is conventional to store, when an abnormality is detected or an unintended behavior is detected for example, vehicle state data indicating vehicle states for retrieving data required for analyzing cause of failure of a vehicle. The vehicle state data is stored only when the abnormality arises or the unintended behavior arises. According to JP-A-H09-126954, a trigger generation device formed of a push button, for example, is provided so that vehicle state data may be stored in response to a trigger signal, which is generated when the trigger generation device is manually operated. The vehicle state data can be stored at an arbitrary time point that the trigger generation device is manually operated.
According to this technology, since the vehicle state data is stored in response to the manual operation on the trigger generation device, the time point of storing the vehicle state data sometimes becomes inappropriate. It is thus not possible in such a case to retrieve accurate vehicle state data required for later analysis.